Media Galleries API: Fix MediaGalleriesPreferences finders race.

chrome/browser/media_galleries/media_file_system_registry_unittest.cc

Index: chrome/browser/media_galleries/media_file_system_registry_unittest.cc
diff --git a/chrome/browser/media_galleries/media_file_system_registry_unittest.cc b/chrome/browser/media_galleries/media_file_system_registry_unittest.cc
index a4f632975c4e314ec5008237c838a34336925fdd..772e21ca5ed8bd768601194e88988028c16bafa0 100644
--- a/chrome/browser/media_galleries/media_file_system_registry_unittest.cc
+++ b/chrome/browser/media_galleries/media_file_system_registry_unittest.cc
@@ -472,7 +472,12 @@ ProfileState::~ProfileState() {
 }
 
 MediaGalleriesPreferences* ProfileState::GetMediaGalleriesPrefs() {
-  return MediaGalleriesPreferencesFactory::GetForProfile(profile_.get());
+  MediaGalleriesPreferences* prefs =
+      MediaGalleriesPreferencesFactory::GetForProfile(profile_.get());
+  base::RunLoop loop;
+  prefs->EnsureInitialized(loop.QuitClosure());
+  loop.Run();
+  return prefs;
 }
 
 void ProfileState::CheckGalleries(
@@ -599,7 +604,11 @@ ProfileState* MediaFileSystemRegistryTest::GetProfileState(size_t i) {
 
 MediaGalleriesPreferences* MediaFileSystemRegistryTest::GetPreferences(
     Profile* profile) {
-  return registry()->GetPreferences(profile);
+  MediaGalleriesPreferences* prefs = registry()->GetPreferences(profile);
+  base::RunLoop loop;
+  prefs->EnsureInitialized(loop.QuitClosure());
+  loop.Run();
+  return prefs;
 }
 
 std::string MediaFileSystemRegistryTest::AddUserGallery(